The present paper outlines the numerical calculation of wave interactions with a thin vertical slotted barrier extending from the water surface to some distance above the seabed, and describes laboratory tests undertaken to assess the numerical model. The numerical model is based on an eigenfunction expansion method and utilizes a boundary condition at the barrier surface which accounts for energy dissipation within the barrier. Comparisons with previous numerical studies for related situations show close agreement and a selection of results based on the method are presented for the transmission, reflection, and energy dissipation coefficients for a partially submerged porous barrier. In addition preliminary comparisons with experimental measurements are given and the choice of suitable friction and added mass coefficients to model the permeability of the breakwater is described.
Breakwaters are widely used to provide economical protection from waves in harbours and marinas. In certain situations, breakwaters in the form of thin, rigid, pile-supported vertical barriers which extend some distance down from the water surface have been used or considered. These have the advantages of allowing water circulation, fish passage and sediment transport beneath the breakwater, and may be relatively economical by providing protection closer to the water surface where wave action is most pronounced. Predictions of wave interactions with such structures have been obtained previously by a number of authors for the case of an impermeable barrier on the basis of linear wave diffraction theory (e.g. Liu and Abbaspour, 1982, Losada et al. 1992, and Abul-Azm, 1993). In some instances, a permeable barrier, such as a slotted vertical barrier made from timber planks, may be preferred. For example, this may be selected in an effort to reduce unwanted wave reflections on the upwave side of the barrier.
